1994 Toyota 4X4, auto, 4 cylinder

HEEEEELP! I know I'm losing coolant somewhere, have been for a while, just keep adding fluid. The other day the vehicke started to overheat, stopped, let it cool down and added fluid to top it off, probably took about 3/4 gallon. I started the vehicle to let it circulate, with the radiator cap off, but upon starting, blew coolant everywhere. I stopped the vehicle again, refilled the radiator a second time, put the radiator cap on this time, and drove it home. I thought maybe it was the thermostat sticking, so I replaced it, ran it for awhile, but when I removed the cap this time, fluid started to bubble out of the radiator, so I put the cap and and ran it for awhile, it did not seem to overheat, but maybe just because I had topped the fluid off? The auto repair store where I bought the thermostat stated it may be a head gasket? Do the symptoms seem like a head gasket, or could it be a cracked head? What kind of costs would I be looking at? I don't have money to burn, and not for sure if I should put any funds towards a different vehicle? Thanks in advance. Limey